Crawlspace Insulation in Zone 3 (Warm)
The DOE recommends R-5 for crawlspace insulation in Climate Zone 3 (Warm). This zone has 3,500 heating degree days and 2,000 cooling degree days annually. The typical crawlspace cavity depth is 4 inches. States in Zone 3 include Alabama, Arizona, Arkansas, California, Georgia and 10 more.
Quick Facts
Insulation Comparison for Crawlspace in Zone 3
The table below compares all insulation types for achieving R-5 in the crawlspace of a building in Zone 3 (Warm). Types marked "Recommended" are specifically suited for crawlspace applications. Material costs are shown per square foot and per 1,000 square feet for easy budgeting. Labor costs typically add 30 to 100 percent to material costs depending on the insulation type and project complexity.
| Insulation Type | R/Inch | Thickness | $/SqFt | $/1000 SqFt | Fits | Rec. |
|---|---|---|---|---|---|---|
| Extruded Polystyrene (XPS) | R-5 | 1" | $0.90 | $900 | Yes | Yes |
| Open-Cell Spray Foam | R-3.7 | 1.4" | $2.00 | $2,000 | Yes | Yes |
| Closed-Cell Spray Foam | R-6.5 | 0.8" | $4.00 | $4,000 | Yes | Yes |
| Blown-In Cellulose | R-3.5 | 1.4" | $0.35 | $350 | Yes | - |
| Blown-In Fiberglass | R-2.5 | 2" | $0.40 | $400 | Yes | - |
| Vermiculite (Loose Fill) | R-2.1 | 2.4" | $0.50 | $500 | Yes | - |
| Fiberglass Batt | R-3.2 | 1.6" | $0.60 | $600 | Yes | - |
| Expanded Polystyrene (EPS) | R-3.9 | 1.3" | $0.60 | $600 | Yes | - |
| Mineral Wool Batt | R-3.3 | 1.5" | $0.75 | $750 | Yes | - |
| Cotton Denim (Recycled) | R-3.5 | 1.4" | $1.00 | $1,000 | Yes | - |
| Polyisocyanurate (Polyiso) | R-6 | 0.8" | $1.10 | $1,100 | Yes | - |
| Mineral Wool Board | R-4.3 | 1.2" | $1.25 | $1,250 | Yes | - |
| Sheep Wool | R-3.5 | 1.4" | $1.75 | $1,750 | Yes | - |
| Aerogel Blanket | R-10 | 0.5" | $15.00 | $15,000 | Yes | - |
Installation Guidance
Crawlspace insulation at R-5 in Zone 3 is best implemented as part of a sealed, conditioned crawlspace design. Apply rigid XPS or closed-cell spray foam to the crawlspace walls from the top of the wall to the footing, achieving the full R-5 requirement. Install a minimum 6-mil polyethylene vapor barrier on the ground floor, overlapping seams by at least 12 inches and sealing all edges to the foundation wall with sealant or tape. Provide conditioning to the crawlspace with a small supply air duct from the HVAC system or a standalone dehumidifier to control moisture levels. If a vented crawlspace design is required by local code, insulate the floor above instead (see the floor insulation recommendations) and ensure that all ductwork and plumbing in the crawlspace is properly insulated.
States in Zone 3
The following states include areas within Climate Zone 3. Click any state to see its complete insulation requirements across all applicable zones.